Amplitude-Frequency spectrum

I am tasked to find the amplitude of the first harmonic of a square wave.  1. I did a time domain fourier series and plot a frequency spectrum

2. I also did a frequency domain fourier series and plot a frequency spectrum.

I realised both frequency spectrums differ by half. May I know which is the correct representation of the frequency spectrum?.

• If you use Google, you possibly get a faster answer. – Long Pham Feb 15 at 18:13
• Well, we won't be able to tell you what you did wrong (and if) without you telling us what formulas exactly make up your time and frequency domain Fourier Series. I honestly only know one Fourier series, so I must admit I'm confused what you're doing. – Marcus Müller Feb 15 at 18:16
• What do you mean by time domain fourier series? In your answer I only see frequency domain plots. The difference of two might be arising because you are using negative frequencies in one case. – sarthak Feb 15 at 18:17
• I recall the two values: 4 and PI, being used as a scale factor. – analogsystemsrf Feb 16 at 4:10